Long term evolution-advanced (LTE-A) is a system further evolved and enhanced from a 3GPP LTE system. In the LTE-A system, a carrier aggregation (CA) technology is introduced to satisfy the requirement of the International Telecommunication Union for the peak data rate of the fourth generation communications technology. The carrier aggregation technology is also referred to as a spectrum aggregation technology or a bandwidth extension technology.
In carrier aggregation, spectrums of two or more component carriers are aggregated to form an aggregated carrier to obtain a wider transmission bandwidth. Spectrums of component carriers in the aggregated carrier may be contiguous continuous spectrums, or may be non-contiguous spectrums in a same frequency band or even discontinuous spectrums in different frequency bands. For the aggregated carrier, an LTE Rel-8/9 user equipment (UE) can access only one of component carriers to transmit and receive data, but an LTE-A UE can access multiple component carriers simultaneously according to its own capability and service requirement to transmit and receive data.
In the carrier aggregation, to support technologies such as dynamic scheduling, downlink multiple input multiple output (MIMO) transmission, and hybrid automatic repeat request, the UE needs to fed back multiple types of uplink control information (UCI) to a base station through a physical uplink control channel (PUCCH), where the UCI includes channel state information (CSI), a HARQ-ACK, a scheduling request (SR), and so on, where the HARQ-ACK may also be simply referred to as an ACK (acknowledgement)/NACK (negative acknowledgement) and the SR is used by the UE to request resources for uplink data sending from the base station.
In the prior art, during carrier aggregation, carriers in a macro base station and a micro base station that have an ideal backhaul may be aggregated. For example, if the macro base station and micro base station are connected through optical fibers, where the micro base station is implemented by using a radio head and an ideal backhaul exists between the macro base station and the micro base station, data may be transmitted between the macro base station and the micro base station in real time. Multiple carries in the macro base station and micro base station may be scheduled jointly, that is, the macro base station also knows the scheduling condition on another component carrier when scheduling one component carrier in the aggregated carrier. In this case, when the UE feeds back a HARQ-ACK to the micro base station, generally the UE sends the HARQ-ACK to the macro base station through a PUCCH on an uplink primary carrier corresponding to the macro base station, and then the macro base station forwards the HARQ-ACK to the micro base station. Because an ideal backhaul exists between the macro base station and the micro base station, both the macro base station and the micro base station can obtain in real time the HARQ-ACK fed back by the UE.
With the continuous development of technologies, carrier aggregation between base stations having a non-ideal backhaul will be introduced in the LTE-A system, where the base stations having a non-ideal backhaul may be two macro base stations, or a macro base station and a micro base station, or two micro base stations, and so on. At present, the prior art has not disclosed a method for transmitting a HARQ-ACK between a UE and a base station in a case where carrier aggregation is performed between base stations having a non-ideal backhaul.